[CostModel] Replace ShuffleKind::SK_Alternate with ShuffleKind::SK_Select (PR33744)

As discussed on PR33744, this patch relaxes ShuffleKind::SK_Alternate which requires shuffle masks to only match an alternating pattern from its 2 sources:

e.g. v4f32: <0,5,2,7> or <4,1,6,3>

This seems far too restrictive as most SIMD hardware which will implement it using a general blend/bit-select instruction, so replaces it with SK_Select, permitting elements from either source as long as they are inline:

e.g. v4f32: <0,5,2,7>, <4,1,6,3>, <0,1,6,7>, <4,1,2,3> etc.

This initial patch just updates the name and cost model shuffle mask analysis, later patch reviews will update SLP to better utilise this - it still limits itself to SK_Alternate style patterns.

Differential Revision: https://reviews.llvm.org/D47985

llvm-svn: 334513

1 files changed, 6 insertions, 6 deletions

diff --git a/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp b/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
index c387b75f122..f26ccdddc85 100644
--- a/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
@@ -400,8 +400,8 @@ int ARMTTIImpl::getAddressComputationCost(Type *Ty, ScalarEvolution *SE,
 
 int ARMTTIImpl::getShuffleCost(TTI::ShuffleKind Kind, Type *Tp, int Index,
                                Type *SubTp) {
-  // We only handle costs of reverse and alternate shuffles for now.
-  if (Kind != TTI::SK_Reverse && Kind != TTI::SK_Alternate)
+  // We only handle costs of reverse and select shuffles for now.
+  if (Kind != TTI::SK_Reverse && Kind != TTI::SK_Select)
     return BaseT::getShuffleCost(Kind, Tp, Index, SubTp);
 
   if (Kind == TTI::SK_Reverse) {
@@ -426,9 +426,9 @@ int ARMTTIImpl::getShuffleCost(TTI::ShuffleKind Kind, Type *Tp, int Index,
 
     return BaseT::getShuffleCost(Kind, Tp, Index, SubTp);
   }
-  if (Kind == TTI::SK_Alternate) {
-    static const CostTblEntry NEONAltShuffleTbl[] = {
-        // Alt shuffle cost table for ARM. Cost is the number of instructions
+  if (Kind == TTI::SK_Select) {
+    static const CostTblEntry NEONSelShuffleTbl[] = {
+        // Select shuffle cost table for ARM. Cost is the number of instructions
         // required to create the shuffled vector.
 
         {ISD::VECTOR_SHUFFLE, MVT::v2f32, 1},
@@ -445,7 +445,7 @@ int ARMTTIImpl::getShuffleCost(TTI::ShuffleKind Kind, Type *Tp, int Index,
         {ISD::VECTOR_SHUFFLE, MVT::v16i8, 32}};
 
     std::pair<int, MVT> LT = TLI->getTypeLegalizationCost(DL, Tp);
-    if (const auto *Entry = CostTableLookup(NEONAltShuffleTbl,
+    if (const auto *Entry = CostTableLookup(NEONSelShuffleTbl,
                                             ISD::VECTOR_SHUFFLE, LT.second))
       return LT.first * Entry->Cost;
     return BaseT::getShuffleCost(Kind, Tp, Index, SubTp);